1. Field
The present invention relates to a method of fabricating a semiconductor device, which is usable to form a microscopic pattern on a semiconductor substrate.
2. Related Art
In fabricating a memory with a high integration degree as a semiconductor device, for example, the memory needs to be microstructured. For this purpose, methods have been proposed to form patterns with microscopic pitches. These patterns are more microscopic than resolution limitations of current lithography techniques.
A sidewall transfer process is known as one of the aforesaid microscopic pattern forming methods. For example, U.S. Pat. No. 7,291,560 discloses a sidewall transfer process. In the disclosed sidewall transfer process, a first film is formed on a processed film and thereafter, the first film is etched and then patterned so that an upper surface of the processed film is exposed.
Subsequently, a second film having a higher selectivity than the first film is formed along an upper surface and side surfaces of the first film and the exposed upper surface of the processed film. The second film is anisotropically etched until the upper surface of the first film is exposed. Subsequently, the first film serving as a core material is removed, whereby a pattern is formed based on the second film.
Since the aforesaid second film is previously formed along the side surfaces of the first film, the second film is formed into an asymmetric shape in which the upper surface is inclined from an upper part of the side surface toward an outer lower part of the side surface. This results in alternate provision of two adjacent patterns having smaller and larger distances between upper ends of the patterns.
When the processed film is etched with the above-described pattern serving as a mask, a microloading effect results in differences in the etching depth since an opening width between upper ends of the mask differs. As a result, a difference in a processing shape in the processed film becomes marked.